A comparative analysis of coastal fishery food webs in the Great Barrier Reef region

[摘要] Executive Summary: The waters of the Great Barrier Reef lagoon have been increasingly subjected to nutrient enrichment and increasing sediment loads from coastal river catchments over the past 150 years, posing a threat to the coral reef ecosystem and the fisheries and tourism industries within the region. Substantial efforts are now being made to change land use practices to reduce contaminant loads to the reef.Four ecosystem models were developed, for the Wet Tropics, Burdekin, Fitzroy and Burnett-Mary natural resource management regions, as a step toward quantifying the food web processes that support coastal fish production within the GBR, identifying differences in those processes among climatic regions, and assessing ecosystem components that are most sensitive to changes in nutrient delivery.Fishery catches are dominated by piscivorous species that rely predominantly on pelagic food web pathways, and prawns which rely on benthic pathways, whilst the Burnett-Mary region also provides large catches of detritivorous and herbivorous fish that benefit from primary production by the extensive seagrass beds in this region. Diagnostic indices for coastal food webs displayed strong positive and negative correlations with catchment indicators related to mean annual rainfall and discharge, seagrass area and land use among regions. Modelled scenarios of nutrient enrichment by 10% over 20 years suggest enhanced energy flow through pelagic food web pathways may support increased biomass of zooplanktivorous, benthivorous and piscivorous fish groups, with an increased risk of seagrass shading leading to a regime shift toward phytoplankton dominance and seagrass depletion. Modelled scenarios of nutrient reduction by 10% over 20 years suggest a reduction in both pelagic and benthic food web pathways leading to reductions in fish biomass. The magnitude of biomass changes under different nutrient scenarios varied according to the magnitude of background variation in nutrient supply and primary production in each region, with predicted changes being smallest in the Fitzroy region where the estimated background variation in primary production was greatest. These results support the need for alternative strategies, such as wetland habitat protection, rehabilitation, and compensatory habitat construction, to sustain fish resources as improvements in catchment management reduce nutrient loads discharged to the coast. Without alternative strategies, even a modest reduction in nutrient loads discharged into coastal waters may cause a decline in fish stocks available to coastal fisheries. This study has identified a mis-match between available water quality data and the spatial and temporal resolution of existing information on coastal ecosystems. Data availability on coastal ecosystems in the GBR is patchy in space and time, requiring a number of assumptions when aggregating data to create regional ecosystem models. This mis-match needs to be rectified to improve ability to predict ecosystem responses at higher trophic levels to changes in water quality and catchment management. Further refinement of the models developed in this study will allow them to support the development of policy to sustain coastal ecosystems and fisheries through changes in catchment management to improve water quality.

[发布机构] CSIRO

[学科分类] 地球科学(综合)